B3 - Proteins and mutations

• All proteins are made of long chains of amino acids joined together.
• Proteins have different functions. E.G.

- strucural proteins used to build cells and tissues, eg. collagen

- hormones, which carry messages to control a reaction, e.g. insulin (controls blood sugar levels)

- carrier proteins, e.g. haemogloblin - carries oxygen

- enzymes

• Each protein has it's own number and order of amino acids. This makes each protein molecule a different shape and gives it a different function.

• Enzymes speed up reactions in the body and are therefore called biological catalysts.
• They catalyse chemical reactions occuring in respiration, photosynthesis and protein synthesis of living cells.
• The substrate molecule fits into the active site of the enzymes like a key a lock

- 'Lock and key mechanism'

- It also explains why each enzyme can only work on a particular substrate. Specificty and it happens becuase the substrate has to be the right shape.

• Enzymes all work best at a particular temperature and pH. This is called the optimum. Any change from the optimum will slow down the reaction.
• Enzyme activity is affected by pH and temperature:

 - At low temperatures molecules are moving slowly so the substrate and enzyme are less likely to collide.

- At very high/low pH values and high temps the enzymes active site changes shape. This is called denaturing. The substrate cannot fit, so cannot react so quickly.

• Mutations can happen on thier own, but can be made to happen by radiation or chemicals.
• When they occur, mutations:

- may lead to the production of different proteins

- are often harmful but may have no effect

- can occasionally give the individual an advantage.

• Although every cell in the body has the same genes it does not mean that all the same proteins are made. This is because different genes are switched off in different cells. This allows different cells to perform different functions.
• Gene mutations alter or prevent the production of the protein that is normally made, because they change the base code of DNA, and so change the order of amino acids in the protein.